Effects of pretreatment methods on properties of activated carbon from rice husk

Abstract: This paper followed the steps below for sample preparation. Rice husk (RH) was taken as the raw material, 10 g rice husk mixed with 200 mL water at 180 ℃ and 1.1 MPa for 1 h in a hydrothermal reactor. By the steps of cooling, filtration, washing to neutral, drying, the water-heated rice husk was obtained. 200 mL of 15% Na2CO3 solution put into 10 g water-heated rice husk and with 2 h desiliconization at 80-100 ℃, washed in water at 80 ℃ until it turn to neutral, then drying and hydrothermal desiliconization pretreated rice husk (STRH) was obtained. 5 g STRH was put in 50 mL FeCl3 solution with a concentration of 0.02 g/mL, then with ultrasonic immersed for 3 h at room temperature, evaporating the water on a rotary evaporator, adding magnetizing agent, the rice husk after magnetization (MSTRH) was obtained. And the rice husk after activition (MSTRH-1) was made by 5 g MSTRH mixing with 50 mL ZnCl2 solution with a concentration of 0.1 g/mL and then following the steps as MSTRH. The difference between with MSTRH and MSTRH-1 was activating agent was added at the end of the preparation of MSTRH-1. The MSTRH-1 was activated at 600 ℃ for 2 h in a nitrogen atmosphere with volume flow of 200 mL/min. All the solid products were washed with dilute hydrochloric acid and then washed with deionized water until neutral, after drying the magnetic activated carbon was obtained, they were named by RHC, STRHC, MSTRHC and MSTRHC-1. The pretreated rice husk and activated carbon were characterized and analyzed to investigate the effects of different pretreatment methods on the preparation of magnetic activated carbon. In the study, the parameter such as high calorific value, surface functional group, thermo gravimetric curve crystal structure, specific surface area and pore structure, specific surface area and pore structure, surface morphology, magnetic performance were measured by calorimeter (SDACM3000), fourier transform infrared spectroscopy (FTIR, Bruker Vector 22), thermogravimetric analyzer (TG, TherMax), X-ray diffractometer (XRD, X'TRA), automatic micropore physisorption analyzer (BET, ASAP 2020M), scanning electron microscope(SEM, LEO1530VP), vibrating sample magnetometer (VSM, Lakeshore7407). The performance of different pretreated rice husk and magnetic activated carbon could be compared. All measurements were taken 3 times. The Na2CO3 catalyzed the pyrolysis of rice husk, which expanded the pore structure, and the dehydration and decarbonylation during hydrothermal reduces oxygen containing groups, so the calorific value was increasing. The addition of magnetic agent inhibits the pyrolysis rate of rice husk but improved the pyrolysis yield. After the pretreatment of adding magnetic agent, the tubular carbon structure was formed on the surface, which increased the specific surface area. Fe3O4 increased the magnetic property remarkably. The addition of activating agent promoted rice husk carbonization, and increased solid product yield and greatly improved the pore structure of activated carbon. However, the magnetic property of rice husk and magnetic activated carbon decreased because of the formation of zinc complex, but the product could still be selected by magnetic separation.